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43 results on '"Ogino, Hiraku"'

3. High-energy ultrasonic irradiation effects on the growth and critical current density of top-seeded melt grown single grain YBa2Cu3O7-δ bulk superconductors

Author

Hagiwara, Rikako, primary, Ishibashi, Shinnosuke, additional, Naik, Sugali Pavan Kumar, additional, Ogino, Hiraku, additional, Pęczkowski, Paweł, additional, Ishida, Shigeyuki, additional, Eisaki, Hiroshi, additional, Sakai, Naomichi, additional, Oka, Tetsuo, additional, and Nishio, Taichiro, additional

Published
2022
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5. Investigation of high-energy ultrasonication of RE2BaCuO5(RE = Y, Gd) on the growth and superconducting properties of REBa2Cu3O7−δtop-seeded melt textured bulks

Author

Pavan Kumar Naik, Sugali, primary, Hagiwara, Rikako, additional, Ishibashi, Shinnosuke, additional, Asano, Natsuki, additional, Ogino, Hiraku, additional, Ishida, Shigeyuki, additional, Koblischka, Michael Rudolf, additional, Koblischka-Veneva, Anjela, additional, Tsuchiya, Yoshinori, additional, Kawashima, Kenji, additional, Eisaki, Hiroshi, additional, and Nishio, Taichiro, additional

Published
2022
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6. Sn addition effects on CaKFe4As4 superconductors

Author

Pavan Kumar Naik, S, primary, Ishida, Shigeyuki, additional, Kamiya, Yoshihisa, additional, Tsuchiya, Yoshinori, additional, Kawashima, Kenji, additional, Eisaki, Hiroshi, additional, Iyo, Akira, additional, and Ogino, Hiraku, additional

Published
2020
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8. Sn addition effects on CaKFe4As4 superconductors.

Author

Naik, S Pavan Kumar, Ishida, Shigeyuki, Kamiya, Yoshihisa, Tsuchiya, Yoshinori, Kawashima, Kenji, Eisaki, Hiroshi, Iyo, Akira, and Ogino, Hiraku

Subjects
SUPERCONDUCTORS, CRYSTAL grain boundaries, MAGNETIC fields, MICROSTRUCTURE, TIN alloys
Abstract

The effects of adding low-melting point metals (Pb, Sn, In and Ge) to polycrystalline CaKFe4As4 (CaK1144) superconductors were investigated. We found that Sn is the most stable with CaK1144 among these low-melting point metals. Synthesis conditions as well as the doping quantity of Sn were optimized, and phase stability, microstructures and superconducting properties were investigated. At the optimized sintering temperature of 700 °C, Sn was effectively solidified in grain boundaries (GBs) of the CaK1144 bulk samples and secondary phase formations were not serious in optimized samples. As the Sn amount increased, filling of Sn in the GBs increased up to 30 wt% with homogeneous dispersion. The magnetic field dependence of critical-current density (Jc) was significantly enhanced by 30 wt% Sn addition and decreased with further increase of Sn addition. The filling up of 1144 grain boundaries by the optimal amount of Sn enhanced the Jc from 11.7 kA cm−2 to 21.7 kA cm−2 in a self-field and at 4.2 K. Sn addition was effective both to suppress the impurity phases as well as increase Jc of CaK1144. [ABSTRACT FROM AUTHOR]

Published
2020
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9. Synthesis of CaKFe4As4 bulk samples with high critical current density using a spark plasma sintering technique.

Author

Ishida, Shigeyuki, Naik, S Pavan Kumar, Tsuchiya, Yoshinori, Mawatari, Yasunori, Yoshida, Yoshiyuki, Iyo, Akira, Eisaki, Hiroshi, Kamiya, Yoshihisa, Kawashima, Kenji, and Ogino, Hiraku

Subjects
CRITICAL current density (Superconductivity), CRITICAL currents, SUPERCONDUCTING transitions, IRON-based superconductors, ELECTRICAL resistivity, VICKERS hardness
Abstract

A high density CaKFe4As4 bulk sample was successfully synthesized using a spark plasma sintering (SPS) technique. The density of the synthesized sample was 5.02 g cm−3, corresponding to 96.2% of the theoretical density of CaKFe4As4. Moreover, a reasonably high Vickers hardness of 1 GPa was measured. The electrical resistivity of the SPS bulk sample was as low as approximately 600 μΩ cm at 300 K, which is smaller than that of the ordinary sintered polycrystalline sample by nearly one order of magnitude, and exhibited a sharp superconducting transition with the transition width (ΔTc) less than 2 K, indicating an improved grain connectivity. The critical current density of the SPS bulk sample calculated from the magnetization hysteresis loops (magnetic Jc) reached 18 kA cm−2 at 4.2 K under 5 T, which is the highest among the iron-based superconductor polycrystalline samples reported thus far. [ABSTRACT FROM AUTHOR]

Published
2020
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17. Synthesis and physical properties of Ca1−xRExFeAs2withRE= La–Gd

Author

Sala, Alberto, primary, Yakita, Hiroyuki, additional, Ogino, Hiraku, additional, Okada, Tomoyuki, additional, Yamamoto, Akiyasu, additional, Kishio, Kohji, additional, Ishida, Shigeyuki, additional, Iyo, Akira, additional, Eisaki, Hiroshi, additional, Fujioka, Masaya, additional, Takano, Yoshihiko, additional, Putti, Marina, additional, and Shimoyama, Jun-ichi, additional

Published
2014
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38. Understanding routes for high connectivity in ex situ MgB2 by self-sintering.

Author

Mizutani, Shunsuke, Yamamoto, Akiyasu, Shimoyama, Jun-ichi, Ogino, Hiraku, and Kishio, Kohji

Subjects
MAGNETIC properties of superconductors, FLUX pinning, CRYSTAL defects, POWDER metallurgy, CARBON
Abstract

Artificial promotion of self-sintering was studied to clarify the factors associated with higher intergranular connectivity in ex situ MgB2. Starting MgB2 powders with different magnesium precursor powder size and carbon additive in the form of B4C powder were prepared and used to synthesize sintered bulks to investigate the influences of interface impurities and intragrain lattice defects on self-sintering of MgB2. Laboratory-made high purity MgB2 powder with less oxidized surface and carbon-substituted MgB2 powder were effective to stimulate self-sintering at 900 °C by increasing the specific surface area and enhancing the driving force of mass transfer. Microstructural analyses showed that ex situ MgB2 bulks synthesized from such pretreated powders demonstrated increased sintered grain boundary area with the evolution of intergrain necks. Record high connectivity (35%) was achieved by a sintering period of 24 h, which is one-fourth of the conventional sintering time. The results suggest that carbon substitution stimulates sintering of grain boundaries and increases the upper critical field of the grains; this leads to quantitative and intensive enhancement of flux pinning strength in a high connectivity matrix. [ABSTRACT FROM AUTHOR]

Published
2014
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39. Dramatic effects of chlorine doping on Jc and microstructure of fluorine-free MOD Y123 thin films.

Author

Motoki, Takanori, Shimoyama, Jun-ichi, Yamamoto, Akiyasu, Ogino, Hiraku, Kishio, Kohji, Honda, Genki, and Nagaishi, Tatsuoki

Subjects
THIN films, FLUORINE, CHLORINE, SEMICONDUCTOR doping, METAL organic chemical vapor deposition
Abstract

Chlorine doped Y123 thin films have been successfully prepared by the fluorine-free metal organic decomposition (FF-MOD) method on SrTiO3(100) single crystal substrates. The rectangular Ba2Cu3O4Cl2 (Ba2342) columns were epitaxially grown in the film without degrading crystallinity and transition temperature (Tc) of Y123. Cl-doped Y123 films maintained high Tc of 90.5–91.5 K and they showed higher critical current density (Jc) than the Cl-free films particularly in magnetic fields. The high Jc feature was observed in thick films up to ∼0.93 μm in thickness. In addition, Cl and Hf co-doped Y123 films maintained high crystallinity and showed further improved Jc of 1.1 MA cm−2 at 40 K under 5 T. These suggested that Ba2342 precipitates have two effects on FF-MOD processed Y123 films. One is an increase in pinning force and the other is improvement of crystallinity of Y123 because of the good lattice matching between Y123 and Ba2342. [ABSTRACT FROM AUTHOR]

Published
2014
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40. Towards the Realization of Higher Connectivity in MgB2 Conductors: In-situ or Sintered Ex-situ?

Author

Yamamoto, Akiyasu, Tanaka, Hiroya, Shimoyama, Jun-ichi, Ogino, Hiraku, Kishio, Kohji, and Matsushita, Teruo

Abstract

The two most common types of MgB2 conductor fabrication technique – in-situ and ex-situ – show increasing conflicts concerning the connectivity, an effective current-carrying cross-sectional area. An in-situ reaction yields a strong intergrain coupling with a low packing factor, while an ex-situ process using pre-reacted MgB2 yields tightly packed grains, however, their coupling is much weaker. We studied the normal-state resistivity and microstructure of ex-situ MgB2 bulks synthesized with varied heating conditions under ambient pressure. The samples heated at moderately high temperatures of ∼900 °C for a long period showed an increased packing factor, a larger intergrain contact area and a significantly decreased resistivity, all of which indicate the solid-state self-sintering of MgB2. Consequently the connectivity of the sintered ex-situ samples exceeded the typical connectivity range 5–15% of the in-situ samples. Our results show self-sintering develops the superior connectivity potential of ex-situ MgB2, though its intergrain coupling is not yet fulfilled, to provide a strong possibility of twice or even much higher connectivity in optimally sintered ex-situ MgB2 than in in-situ MgB2. [ABSTRACT FROM AUTHOR]

Published
2012
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42. New Series of Nickel-Based Pnictide Oxide Superconductors (Ni2Pn2)(Sr4Sc2O6) (Pn = P, As).

Author

Matsumura, Yutaka, Ogino, Hiraku, Horii, Shigeru, Katsura, Yukari, Kishio, Kohji, and Shimoyama, Jun-ichi

Abstract

We have discovered new nickel-based pnictide oxide superconductors, (Ni2Pn2)(Sr4Sc2O6) (Pn = P, As). These compounds have a tetragonal unit cell with a space group of P4/nmm and they consist of alternate stacking of anti-fluorite Ni2Pn2 layers and K2NiF4-type Sr4Sc2O6 blocking layers. Lattice parameters were a = 4.044 Å and c = 15.23 Å for (Ni2P2)(Sr4Sc2O6) and a = 4.078 Å and c = 15.41 Å for (Ni2As2)(Sr4Sc2O6), indicating their thicker blocking layers than that of LaNiPO (c∼8.1 Å). Both (Ni2P2)(Sr4Sc2O6) and (Ni2As2)(Sr4Sc2O6) exhibited superconductivity with zero resistivity at 3.3 and 2.7 K, respectively. The perfect diamagnetism observed in both compounds guaranteed their bulk superconductivity. [ABSTRACT FROM AUTHOR]

Published
2009
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43. Tri-axial Grain Orientation of Y2Ba4Cu7Oy Achieved by the Magneto-science Method.

Author

Fukushima, Takayuki, Horii, Shigeru, Ogino, Hiraku, Uchikoshi, Tetsuo, Suzuki, Tohru S., Sakka, Yoshio, Ishihara, Atsushi, Shimoyama, Jun-ichi, and Kishio, Kohji

Abstract

Tri-axial orientation of orthorhombic and twin-free Y2Ba4Cu7Oy (Y247) powders was attempted using a rotating magnetic field with modulated rate. Although magnetic anisotropy of paramagnetic Y247 originated only from the two-dimensional CuO2 and one-dimensional Cu–O chain structures are small, strong tri-axial grain orientation with misorientation angles below 1.5° was successfully achieved during the solidification process of epoxy resin. Our present results indicate the possibility of fabrication of tri- or bi-axial grain-oriented bulk and thick films without applying epitaxial methods, such as melt-solidification or thin film deposition, and that the modulated-rotation magnetic field is applicable not only to RE247 compounds but also to orthorhombic high critical temperature cuprate superconductors, including practical REBa2Cu3Oy, in principle. [ABSTRACT FROM AUTHOR]

Published
2008
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